Nick Clegg has criticised a Labour-led council that sent leaflets to social housing tenants encouraging them to consider fostering a child as a way to avoid the so-called bedroom tax that comes into force next week.

The deputy prime minister was confronted about the issue during his weekly Call Clegg phone-in on LBC radio. He also praised stay-at-home mothers, following complaints that his childcare proposals help only those going to work.

Clegg said: "It is not right for Ealing council to take an exemption that we announced a couple of weeks ago to say foster families will not be covered by this and then to use this to go round locally saying why don't you turn yourselves into a foster family."

He said it was the first he had heard of the leaflets. "I am not happy at all with councils encouraging people to change the way they are as families just to avoid that £14 a week," Clegg said.

The Ealing leaflet says: "Are you a tenant or resident that will be affected by the changes to housing benefit? … If you are in this position, then you could think about using your spare room to foster. Foster children are not counted as part of your household for housing benefit purposes."

The west London council defended the leaflet, saying it would retain a vigorous assessment procedure. "We want as many people as possible to consider fostering and recognise welfare benefit changes may have appeared to be a barrier to some families who could become potential foster parents."

A Department for Work and Pensions spokesman said: "Reforming the spare room subsidy will save the taxpayer around £500m a year. We need to make the best use of our existing social housing stock when there are nearly two million households on the social housing waiting list and over a quarter of a million tenants are living in overcrowded conditions."

Clegg denied during the phone-in that his office had received a complaint of improper conduct about the Lib Dem MP Mike Hancock in 2011. Hancock denies allegations over his conduct.

"My office never received one of the letters from the complainant's solicitors. We did receive a letter in February of this year. The police have looked into this matter before, [and] have dismissed it because they don't think they can take it forward on advice of the Crown Prosecution Service," he said.